Epistles of Le Révérend Docteur

looking at photos like these scares and fascinates me in equal doses. the sheer scale of these holes reminds you of just how tiny you are

Mirny diamond mine, Siberia

I”m pretty sure most people have seen this one. It’s an absolute beast and holds the title of largest open diamond mine in the world. at 525 metres deep with a top diameter of 1200 metres there’s even a no-fly zone above the hole due to a few helicopters being sucked in.

Apparently this fascinated Teh Netizenz who subsequently went ballistic (intended) in the comments.

And here they are, Parishioners!

* * * UPDATE * * *

Deputy Dog has moved and these comments are no longer available. They remain preserved for prosperity here.

From the comments:

Helicopters do not get “sucked into holes”. LOL.

Helicopters hovering over the ground push the air column between them and the ground to stay in the air. If you all of a sudden cross a huge hole the helicopter will drop if it does not increase the speed of the rotors accordingly. (BTW increasing the speed of the rotors to go from 0 to 500+ meters (1700 feet) is not an easy or quick task)

Sorry Mobius, but it is posible that an helicopter gets sucked into a hole, if it is big enough (read deep enough). That is because earth is hotter underground, and if you get deep enough, you get a “Termal Borehole”, when the diference in temperature causes a stream of hot air.
Now, when a helicopter enters such hot air stream, he no longer can sustain his altitude because he is adjusted to the colder air outside of stream, that is thicker then the hot air. The hellicopter is going to fall so long until the pilot adjusts the speed of the rotor to the hot air (if the hole is very deep, the air is to hot and the helicopter is going to fall before the helicopter achives enough power).
There is also a stream of colder air, that streams into such a hole, and again, if a hole is deep enough, that is a powerfull stream that easily slams a helicopter into ground or into the wall of the borehole.
I hope that I gave a good explanation for the hellicopter accidents, and I apologise for a bad english, I do not live in a english speaking area.

MB.. Helicopters do not get their lift by pushing air between them and the ground or else helicopters would not be able to fly hundreds of feet in the air and everyone below the helicopters path on the ground would be blown around… Go study some physics about lift and flight…

“Helicopters hovering over the ground push the air column between them and the ground to stay in the air.”
No, that’s not true. The “air column between them and the ground” only has relevance at low altitude, when the helicopter is hovering in what is called its “ground effect.” In that case, yes, there’s a “cushion” of air built up from the rotor downwash that provides some additional lift.
But that’s only at very low altitudes. Once you’re above that, no, there’s no “air column between them and the ground,” and the helicopter stays in the air the same way fixed-wing aircraft stay in the air: from the airflow over the wings. The only difference is that in a helicopter, the wings are rotating.
Disclaimer: I’m only a helicopter flight test engineer, not an aerodynamicist. This has been simplified for your protection.

MB – sorry – helicopters do NOT “compress the air between them and the ground” (unless flying in ground effect – which is like < 10 ft up) – they fly by LIFT – just like a regular airplane – a helicopter has a pair of LONG skinny WINGS called a rotor – and they spin and provide lift – which is why the technical term for a helicopter is a “rotary wing aircraft”

Funny that they’d put a no-fly zone around hole #1, which just happens to be situated right at the base of the runway to that airport (see third photo, apparently taken from airliners.net)…

“Helicopters hovering over the ground push the air column between them and the ground to stay in the air.” Wrong. Helicopters push air downwards, creating lift, whether there is ground beneath or not. The lift is generated at the blades, not by air bouncing off the ground and pushing the helicopter back up. Think of a boat on a large lake, does the propeller push the water against the shore to create thrust? No. That is stilly. Same concept with helicopters.

A lot of people are talking about a helicopter’s wings pushing down on the air and lifting the helicopter by reactive force. I am not qualified in aerodynamics, but I alwys thought that the lift off a plane’s wing (and the rotors of a helicopter) was from the negative pressure created *above* the wing, rather than pushing the air downwards. That said, I can see how flying across a large hole could cause a loss of lift. Warm air rising from the hole would be less dense than the surrounding air, and reduce the lift available to the rotors – a bit like the air bubbles in a jacuzzi mean you sink further into the water that you do in a swimming pool.

Uf, a disclaimer of some sort. I didn’t say that a helicopter pushes air downwards and so creates a hovering efect. The physics here is rather complicated (some of you are corect with the diference in preasure) but, BEARDY PEARSON explained it great (quote: “A lot of people are talking about a helicopter’s wings pushing down on the air and lifting the helicopter by reactive force. I am not qualified in aerodynamics, but I alwys thought that the lift off a plane’s wing (and the rotors of a helicopter) was from the negative pressure created *above* the wing, rather than pushing the air downwards. That said, I can see how flying across a large hole could cause a loss of lift. Warm air rising from the hole would be less dense than the surrounding air, and reduce the lift available to the rotors – a bit like the air bubbles in a jacuzzi mean you sink further into the water that you do in a swimming pool.” end of quote) This is for the hot air. Considering the cold air, imagine that you are standing on a ~30cm broad board. There is not eaven a clue of wind. And sudently, there comes a strong wind. Normaly, such a broad board is enough for standing, bud so sudent blow of air knock’s you down, if you are not prepared.
If there is a physicist, please help with a explanation. I am to interested in details.

And, finally, I award the last word to:

Wow!! I feel very educated about holes in the earth, which were kinda freaky…..and now I can say I know something about helicopters too. Fascinating.

am fascinated by what i read from this site.with ma little physics i always thought that helicopters rise in the air by rotating their wing thus creating an area of low pressure.this enables it to lift up.does it make sense.